1. Field of the Invention
This invention relates to a two-cycle internal combustion engine of the fuel injection type, and in particular to a two-cycle internal combustion engine of the fuel injection type which is relatively small in size and suited for use in a portable working machine such as a chain saw or a bush cutter.
2. The Prior Art
Because of the increasing concern in recent years of environmental problems, a reduction not only of the toxic substances in the exhaust gas but also of the engine noise is strongly demanded even in a small two-cycle internal combustion engine. In particular, there are pollution problems inherent to a two-cycle internal combustion engine, i.e. a problem of how to reduce the quantity of HC in the exhaust gas which is brought about due to a phenomenon of blow-by of unburnt air-fuel mixture from a combustion chamber, and a problem of how to prevent the discharge of unburnt fuel which is brought about due to a phenomenon of spitting of fuel toward the air-cleaner. These problems are also desired to be solved.
On the other hand, a lean burn engine, or a direct injection engine wherein fuel is directly injected into a combustion chamber has been recently proposed as a four-cycle internal combustion engine. In these types of engine, the reduction of toxic substances in the exhaust gas by means of a lean-burning technique is taken into consideration. Therefore, it is now studied how to apply this technique to a two-cycle internal combustion engine.
For example, a two-cycle internal combustion engine of the direct fuel injection type is proposed in U.S. Pat. No. 4,813,391. According to this technique, a fuel injection nozzle is disposed at a cylinder head portion of the combustion chamber so as to permit the injection of fuel to be effected directly into the combustion chamber. In this case, a fuel pump is actuated taking advantage of the fluctuation in pressure within a crank case, and, through this actuation of the fuel pump, fuel is fed to the fuel injection nozzle and then directly injected into the combustion chamber. The stroke of fuel injection, i.e. the injection of fuel from the injection nozzle, is performed as follows. Namely, as a piston is moved downward, the pressure inside a crank-case is proportionally increased, and when the piston is brought down to approximately the bottom dead center, the fuel pump is actuated by the pressure inside the crank-case, thus feeding fuel to the fuel injection nozzle, from which the fuel is injected by the pressing force of the fuel pump into the combustion chamber.
There is also known another example of a two-cycle internal combustion engine of the direct fuel injection type, wherein a fuel injection nozzle is disposed midway of an air passage (scavenging passage) communicating with a combustion chamber. Fuel from the injection nozzle is injected toward a heat conductive wall constituting a cylinder wall and impinged thereon so as to be gasified and mixed with air passing through the air passage, the resultant air-fuel mixture being fed to a combustion chamber (U.S. Pat. No. 4,876,999).
However, in the case of the former engine of the direct fuel injection type (U.S. Pat. No. 4,813,391), wherein the fuel injection nozzle is mounted on a cylinder body and fuel is directly injected from the fuel injection nozzle into the combustion chamber, the timing and manner of fuel injection are set such that the fuel pump is actuated depending on the pressure change inside the crank-case and the fuel is injected by the delivery pressure of the fuel pump, so that the timing of fuel injection as well as the quantity of fuel to be injected are rather difficult to adjust. At the same time, a fuel pump for injection of fuel as well as an operation system for actuating the fuel pump are required to be employed. Therefore, this fuel injection mechanism is not suited for the combustion control (air/fuel ratio control) of the engine and the structure thereof is rather complicated, thus raising a problem that the manufacturing cost thereof would be increased.
On the other hand, in the case of the injection system of a fuel injection nozzle which is commonly employed in a four-cycle internal combustion engine, fuel is compressed by means of a plunger pump and then fed to the fuel injection nozzle. An electrically operable member such as an electromagnetic solenoid is mounted on the fuel injection nozzle. On the occasion of fuel injection, the electrically operable member is magnetized to open or close the valve of the fuel injection nozzle.
In this fuel injection system, the timing of fuel injection is controlled electrically, thus making it possible to inject fuel at an appropriate timing and to adjust the quantity of fuel. However, it is required according to this system to provide the fuel injection nozzle with an electrically operable member and a nozzle shut-off valve, and at the same time to install a control device for controlling the fuel injection nozzle. These devices which are required in the manufacture of the fuel injection type engine as mentioned above are rather expensive, so that the application of the fuel injection nozzle of this system to a two-cycle internal combustion engine for a bush cutter, etc. is not suitable in terms of cost.